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      <title>Overview of the org.apache.commons.pool component</title>
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      <p>
         Generic Object pooling API with several implementations.
      </p>
      <p>
         The <code>org.apache.commons.pool</code> package defines a simple 
         interface for a pool of object instances, and a handful of base 
         classes that may be useful when creating pool implementations.
         The api supports pooling of unique objects which can be requested
         via a key as well as pools where all objects are equivalent.
      </p>
      <p>
         The <code>org.apache.commons.pool.impl</code> package contains
         several pool implementations.  
         {@link org.apache.commons.pool.impl.StackObjectPool StackObjectPool}
         is useful for supporting reuse of a limited number of instances while
         allowing new instances to be created as needed to support high demand.
         {@link org.apache.commons.pool.impl.GenericObjectPool 
         GenericObjectPool} has many configuration options and can support
         a limited set of objects such as would be useful in a database
         connection pool.
         {@link org.apache.commons.pool.impl.SoftReferenceObjectPool 
         SoftReferenceObjectPool} has no limit on the number of objects in the
         pool, but garbage collector can remove idle objects from the pool as
         needed.  There are also keyed versions of the first two.
      </p>
      <p>
         Here is a simple example of pooling <code>HashMap</code>'s.  First 
         create an {@link org.apache.commons.pool.ObjectPoolFactory 
         ObjectPoolFactory}
      </p>
<pre>
    public class HashMapFactory 
        extends {@link org.apache.commons.pool.BasePoolableObjectFactory BasePoolableObjectFactory}
    {
        /**
         * Creates an instance that can be returned by the pool.
         * @return an instance that can be returned by the pool.
         */
        public Object makeObject() 
            throws Exception
        {
            return new HashMap();
        }
        
        /**
         * Uninitialize an instance to be returned to the pool.
         * @param obj the instance to be passivated
         */
        public void passivateObject(Object obj) 
            throws Exception
        {
            Map map = (Map)obj;
            map.clear();
        }
    }
</pre>
      <p>
         A class that makes frequent use of a Map could then use a pool
         as shown below:
      </p>
<pre>
    public class Foo
    {
        private {@link org.apache.commons.pool.ObjectPool ObjectPool} pool;
        public Foo()
        {
            {@link org.apache.commons.pool.PoolableObjectFactory PoolableObjectFactory} factory = new HashMapFactory();
            pool = new StackObjectPool(factory, 1000);
        }

        public doSomething()
        {
            ...
            Map map = null;
            try
            {
                map = (Map)pool.borrowObject();
                // use map
                ...
            }
            finally
            {
                if (map != null)
                {
                    pool.returnObject(map);
                }
            }
            ...
        }
    }
</pre>

<p>
The above example shows how one would use an 
{@link org.apache.commons.pool.ObjectPool ObjectPool}.  The other supplied 
implementations or another special purpose pool would be used similarly.
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